Crystal‐Facet‐Engineered BiOBr(1 1 0)/MXene Sponge–Hydrogel Evaporators for Synergistic Solar Desalination and Non‐Mineralizing Volatile Organic Compound Conversion

Abstract

Solar‐driven interfacial evaporation (SDIE) systems face critical challenges associated with volatile organic compound (VOC) contamination in condensate and salt accumulation. Herein, a photothermal–photocatalytic BiOBr/MXene nanocomposite evaporator is engineered via crystal‐facet engineering and biphasic structural design to enable the directional conversion of toluene into nonvolatile products. The melamine sponge‐hydrogel substrate integrates MXene (97.25% solar absorption) with reactive BiOBr(1 1 0) facets, achieving an evaporation rate of 2.42 kg m −2  h −1 under 1 sun irradiation while driving stepwise toluene oxidation. Within 1 h, toluene is selectively converted to benzaldehyde, followed by oxidation to benzoic acid over 12 h. In situ spectroscopy and density functional theory (DFT) calculations reveal that oxygen vacancies and Lewis acid sites on BiOBr(1 1 0) enhance toluene adsorption, whereas a built‐in electric field promotes photogenerated carrier separation, thereby facilitating radical‐chain reactions and suppressing VOC volatilization through conversion into high‐boiling‐point polar products. The biphasic structure further resists salt crystallization for 7 days in 14 wt.% brine through capillary‐swelling transport and dynamic salt regulation, concurrently enabling >99.999% heavy metal removal and phenol degradation efficiencies of up to 99.0%. This work proposes a “conversion‐over‐mineralization” strategy, synergizing high‐efficiency evaporation, salt resistance, and water safety for practical solar‐driven purification.